Fluids, which may be in liquid or gas state, are often transported, distributed, and/or sold to customers through a system of transmission and distribution lines. For purposes such as billing and inventory control, for example, fluid flow measurement systems may be installed at various locations along these lines. Gas metering systems, for example, may measure the volume of gas that flows through a particular gas line. Fluid measurement systems typically include a fluid flow meter and an electronic or mechanical indicator or index.
As an illustrative example, one type of fluid flow meter is a rotary meter for measuring a volume of gas through a gas line. In some rotary meters, gas flowing through the meter causes a set of impellers to rotate within a cylinder. This type of meter is normally referred to as a rotary positive displacement meter. As the impellers turn, they measure a displaced volume of gas that is fixed and determined by the area between the impeller and cylinder. Each impeller rotation indicates that a certain volume of gas has flowed through the meter. This is normally referred to as “actual” volume as measured by the primary flow element that is in this case a rotary positive displacement meter. Buying and selling of natural gas typically requires that the actual volume be converted to “standard” volume to account for the contraction or expansion of gas due to varying gas pressure and gas temperature. In general, these effects may be described by Boyle's and Charles' Law. To convert actual volume to standard volume, some gas metering systems use an electronic volume corrector to correct actual volume measurement originating from the rotating impellers to account for temperature or pressure of the gas in the meter.
In general, fluid flow measurement systems often can be applied in harsh conditions, subject to extremes in temperatures, weather, contaminants, and/or mechanical vibration. Furthermore, some fluid flow measurement systems may be installed in locations that are remote or otherwise difficult to access for maintenance purposes. Moreover, electronics to provide volume correction functions consume electrical power for which batteries may be the only readily available source.
Accordingly, maintaining fluid flow measurement systems that operate from battery power can require battery related maintenance. Batteries can have various electrical and/or mechanical failure mechanisms. For example, batteries can develop leaks, depleted charge, short circuits, overheating, high internal resistance, or open circuits. Moreover, contacts may fail to provide sufficient continuity to the battery terminals due to contamination or vibration. A significant portion of the lifetime cost of maintaining some liquid and gas fluid flow measurement systems may be attributable to battery-related faults.